The present invention is directed to hot melt ink compositions. More specifically, the present invention is directed to ink compositions that are solid at room temperature and that are suitable for ink jet printing processes, particularly thermal ink jet printing processes. One embodiment of the present invention is directed to a hot melt ink composition comprising (a) an ink vehicle, said ink vehicle being a solid at about 25.degree. C. and having a viscosity of from about 1 to about 20 centipoise at a temperature suitable for hot melt ink jet printing, said temperature being greater than about 45.degree. C., (b) a photochromic material, (c) an optional colorant, and (d) an optional propellant.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, they are much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The second type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink-filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be retired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described, for example, in U.S. Pat. Nos. 4,601,777; 4,251,824; 4,410,899; 4,412,224; and 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
Ink jet printing processes may also employ inks that are solid at room temperature and liquid at elevated temperatures. For example, U.S. Pat. No. 4,490,731, the disclosure of which is totally incorporated herein by reference, discloses an apparatus for dispensing solid ink for printing on a substrate such as paper. The ink dye vehicle is chosen to have a melting point above room temperature, so that the ink which is melted in the apparatus will not be subject to evaporation or spillage during periods of nonprinting. The vehicle is also chosen to have a low critical temperature to permit the use of the solid ink in a thermal ink jet printer. In thermal ink jet printing processes employing hot melt inks, the solid ink is melted by the heater in the printing apparatus and utilized as a liquid in a manner similar to that of conventional thermal ink jet printing. Upon contact with the printing substrate, the molten ink solidifies rapidly, enabling the dye to remain on the surface instead of being carried into the paper by capillary action, thereby enabling higher print density than is generally obtained with liquid inks. Advantages of a hot melt ink in ink jet printing are elimination of potential spillage of the ink during handling, a wide range of print density and quality, minimal paper cockle or distortion, and enablement of indefinite periods of nonprinting without the danger of nozzle clogging, even without capping the nozzles.
In addition, U.S. Pat. No. 4,751,528, the disclosure of which is totally incorporated herein by reference, discloses a hot melt ink jet system which includes a temperature-controlled platen provided with a heater and a thermoelectric cooler electrically connected to a heat pump and a temperature control unit for controlling the operation of the heater and the heat pump to maintain the platen temperature at a desired level. The apparatus also includes a second thermoelectric cooler to solidify hot melt ink in a selected zone more rapidly to avoid offset by a pinch roll coming in contact with the surface of the substrate to which hot melt ink has been applied. An airtight enclosure surrounding the platen is connected to a vacuum pump and has slits adjacent to the platen to hold the substrate in thermal contact with the platen.
Further, U.S. Pat. No. 4,791,439, the disclosure of which is totally incorporated by reference, discloses an apparatus for use with hot melt inks having an integrally connected ink jet head and reservoir system, the reservoir system including a highly efficient heat conducting plate inserted within an essentially non-heat conducting reservoir housing. The reservoir system has a sloping flow path between an inlet position and a sump from which ink is drawn to the head, and includes a plurality of vanes situated upon the plate for rapid heat transfer.
U.S. Pat. No. 5,006,170 (Schwarz) and U.S. Pat. No. 5,122,187 (Marchessault et al.), the disclosures of each of which are totally incorporated herein by reference, disclose hot melt ink compositions suitable for ink jet printing which comprise a colorant, a binder, and a propellant selected from the group consisting of hydrazine; cyclic amines; ureas; carboxylic acids; sulfonic acids; aldehydes; ketones; hydrocarbons; esters; phenols; amides; imides; halocarbons; urethanes; ethers; sulfones; sulfamides; sulfonamides; phosphites; phosphonates; phosphates; alkyl sulfides; alkyl acetates; and sulfur dioxide. Also disclosed are hot melt ink compositions suitable for ink jet printing which comprise a colorant, a propellant, and a binder selected from the group consisting of rosin esters; polyamides; dimer acid amides; fatty acid amides; epoxy resins; fluid paraffin waxes; fluid microcrystalline waxes; Fischer-Tropsch waxes; polyvinyl alcohol resins; polyols; cellulose esters; cellulose ethers; polyvinyl pyridine resins; fatty acids; fatty acid esters; poly sulfonamides; benzoate esters; long chain alcohols; phthalate plasticizers; citrate plasticizers; maleate plasticizers; sulfones; polyvinyl -pyrrolidinone copolymers; polyvinyl pyrrolidone/polyvinyl acetate copolymers; novalac resins; natural product waxes; mixtures of linear primary alcohols and linear long chain amides; and mixtures of linear primary alcohols and fatty acid amides. In one embodiment, the binder comprises a liquid crystalline material.
Photochromism in general is a reversible change of a single chemical species between two states having distinguishably different absorption spectra, wherein the change is induced in at least one direction by the action of electromagnetic radiation. The inducing radiation, as well as the changes in the absorption spectra, are usually in the ultraviolet, visible, or infrared regions. In some instances, the change in one direction is thermally induced. The single chemical species can be a molecule or an ion, and the reversible change in states may be a conversion between two molecules or ions, or the dissociation of a single molecule or ion into two or more species, with the reverse change being a recombination of the two or more species thus formed into the original molecule or ion. Photochromic phenomena are observed in both organic compounds, such as anils, disulfoxides, hydrazones, osazones, semicarbazones, stilbene derivatives, o-nitrobenzyl derivatives, spiro compounds, and the like, and in inorganic compounds, such as metal oxides, alkaline earth metal sulfides, titanates, mercury compounds, copper compounds, minerals, transition metal compounds such as carbonyls, and the like. Photochromic materials are known in applications such as photochromic glasses, which are useful as, for example, ophthalmic lenses.
Methods for encoding machine-readable information on documents, packages, machine parts, and the like, are known. One-dimensional symbologles, such as those employed in bar codes, are known. Two-dimensional symbologles generally are of two types--matrix codes and stacked bar codes. Matrix codes typically consist of a random checker board of black and white squares. Alignment features such as borders, bullseyes, start and stop bits, and the like, are included in the matrix to orient the matrix during scanning. Stacked bar codes consist of several one-dimensional bar codes stacked together. Two-dimensional symbologles have an advantage over one-dimensional symbologles of enabling greater data density. For example, a typical bar code can contain from about 9 to about 20 characters per inch, while a typical two-dimensional symbology can contain from about 100 to about 800 characters per square inch. Many two-dimensional symbologles also utilize error correction codes to increase their robustness. Examples of two-dimensional symbologles include PDF417, developed by Symbol Technologies, Inc., Data Matrix, developed by International Data Matrix, Vericode, developed by Veritec, Inc., CP Code, developed by Teiryo, Inc. and Integrated Motions, Inc., Maxicode, developed by the United Parcel Service, Softstrip, developed by Softstrip, Inc., Code One, developed by Laserlight Systems, Supercode, developed by Metanetics Inc., DataGlyph, developed by Xerox Corporation, and the like. One-dimensional and two-dimensional symbologles can be read with laser scanners or with video cameras. The scanners typically consist of an imaging detector coupled to a microprocessor for decoding. Scanners can be packaged into pen-like pointing devices or guns. Bar-like codes and methods and apparatus for coding and decoding information contained therein are disclosed in, for example, U.S. Pat. No. 4,692,603, U.S. Pat. No. 4,665,004, U.S. Pat. No. 4,728,984, U.S. Pat. No. 4,728,783, U.S. Pat. No. 4,754,127, and U.S. Pat. No. 4,782,221, the disclosures of each of which are totally incorporated herein by reference.
European Patent Application 469,864-A2 (Bloomberg et al.), the disclosure of which is totally incorporated herein by reference, discloses self-clocking glyph shape codes for encoding digital data in the shapes of glyphs that are suitable for printing on hardcopy recording media. Advantageously, the glyphs are selected so that they tend not to degrade into each other when they are degraded and/or distorted as a result, for example, of being photocopied, transmitted via facsimile, and/or scanned into an electronic document processing system. Moreover, for at least some applications, the glyphs desirably are composed of printed pixel patterns containing nearly the same number of on pixels and nearly the same number of off pixels, such that the code that is rendered by printing such glyphs on substantially uniformly spaced centers appears to have a generally uniform texture. In the case of codes printed at higher spatial densities, this texture is likely to be perceived as a generally uniform gray tone. Binary image processing and convolution filtering techniques for decoding such codes are also disclosed.
European Patent Application 459,792-A2 (Zdybel et al.), the disclosure of which is totally incorporated herein by reference, discloses the provision in electronic document processing systems for printing unfiltered or filtered machine-readable digital representations of electronic documents, and human-readable renderings of them on the same record medium using the same printing process. The integration of machine-readable digital representations of electronic documents with the human-readable hardcopy renderings of them may be employed, for example, not only to enhance the precision with which the structure and content of such electronic documents can be recovered by scanning such hardcopies into electronic document processing systems, but also as a mechanism for enabling recipients of scanned-in versions of such documents to identify and process annotations that were added to the hardcopies after they were printed and/or for alerting the recipients of the scanned-in documents to alterations that may have been made to the original human-readable content of the hardcopy renderings. In addition to storage of the electronic representation of the document, provision is made for encoding information about the electronic representation of the document itself, such as file name, creation and modification dates, access and security information, and printing histories. Provision is also made for encoding information which is computed from the content of the document and other information, for purposes of authentication and verification of document integrity. Provision is also made for the encoding of information which relates to operations which are to be performed depending on handwritten marks made upon a hardcopy rendering of the document; for example, encoding instructions of what action is to be taken when a box on a document is checked. Provision is also made for encoding in the hardcopy another class of information: information about the rendering of the document specific to that hardcopy, which can include a numbered copy of that print, the identification of the machine which performed that print, the reproduction characteristics of the printer, and the screen frequency and rotation used by the printer in rendering halftones. Provision is also made for encoding information about the digital encoding mechanism itself, such as information given in standard-encoded headers about subsequently compressed or encrypted digital information.
U.S. Pat. No. 5,128,525 (Stearns et al.), the disclosure of which is totally incorporated herein by reference, discloses weighted and unweighted convolution filtering processes for decoding bitmap image space representations of self-clocking glyph shape codes and for tracking the number and locations of the ambiguities or "errors" that are encountered during the decoding. This error detection may be linked to or compared against the error statistics from an alternative decoding process, such as the binary image processing techniques that are described to increase the reliability of the decoding that is obtained.
U.S. Pat. No. 5,291,243 (Heckman et al.), the disclosure of which is totally incorporated herein by reference, discloses a system for printing security documents which have copy detection or tamper resistance in plural colors with a single pass electronic printer printing an integrated image controlled by an image generation system which electronically generates a safety background image pattern with first and second interposed color patterns which is electronically merged with alphanumeric information and a protected signature into an integrated electronic image for the printer. The single pass printer preferably has an imaging surface upon which two latent images thereof are interposed, developed with two differently colored developer materials, and simultaneously transferred to the substrate in a single pass. The color patterns are preferably oppositely varying density patterns of electronically generated pixel dot images with varying spaces therebetween. Preferably a portion of the alphanumeric information is formed by a special secure font, such as a low density shadow copy. The validating signature also preferably has two intermixed color halftone patterns with halftone density gradients varying across the signature in opposite directions, but differently from the background. Also electronically superimposed in the safety background pattern may be substantially invisible latent image pixel patterns which become visible when copied, and/or are machine readable even in copies.
U.S. Pat. No. 5,168,147 (Bloomberg), the disclosure of which is totally incorporated herein by reference, discloses binary image processing techniques for decoding bitmap image space representations of self-clocking glyph shape codes of various types (e.g., codes presented as original or degraded images, with one or a plurality of bits encoded in each glyph, while preserving the discriminability of glyphs that encode different bit values) and for tracking the number and locations of the ambiguities (sometimes referred to herein as "errors") that are encountered during the decoding of such codes. A substantial portion of the image processing that is performed in the illustrated embodiment of the invention is carried out through the use of morphological filtering operations because of the parallelism that is offered by such operations. Moreover, the error detection that is performed in accordance with this invention may be linked to or compared against the error statistics from one or more alternative decoding process, such as the convolution filtering process that is disclosed herein, to increase the reliability of the decoding that is obtained.
U.S. Pat. No. 5,091,966 (Bloomberg et al.), the disclosure of which is totally incorporated herein by reference, discloses weighted and unweighted convolution filtering processes for decoding bitmap image space representations of self-clocking glyph shape codes and for tracking the number and locations of the ambiguities or "errors" that are encountered during the decoding. This error detection may be linked to or compared against the error statistics from an alternative decoding process, such as the binary image processing techniques that are described to increase the reliability of the decoding that is obtained.
U.S. Pat. No. 5,051,779 (Hikawa), the disclosure of which is totally incorporated herein by reference, discloses an image processing system which specifies input image information on the basis of existence of a special mark or patterns printed on a job control sheet. Selected one of various image processings is executed in accordance with the existence of the special mark or patterns to thereby obtain output image information. Each of the special marks or patterns are line drawings, each drawn so as to have a certain low correlative angle to the longitudinal and transverse directions of an image provided with the special mark or patterns.
U.S. Pat. No. 5,337,361 (Wang et al.), the disclosure of which is totally incorporated herein by reference, discloses a record which contains a graphic image and an information area which are interrelated to discourage misuse of the record. The information area can overlay the graphic image and include information encoded in an error-correctable, machine-readable format which allows recovery of the information despite distortion due to the underlying graphic image. The record may also represent the image by words similar in form to words in the information area. Both the information and graphic words can then be altered when an action regarding the record takes place.
Copending application U.S. Ser. No. 08/567,786, filed concurrently herewith, entitled "Method for Embedding and Recovering Machine-Readable Information," with the named inventors Trevor I. Martin and John F. Oliver, the disclosure of which is totally incorporated herein by reference, discloses a method of embedding and recovering machine readable information on a substrate which comprises (a) writing data in a predetermined machine readable code format on the substrate with a photochromic marking material having a first state corresponding to a first absorption spectrum and a second state corresponding to a second absorption spectrum; and (b) thereafter effecting a photochromic change in the photochromic marking material from the first state to the second state.
Copending application U.S. Ser. No. 08/567,637, filed concurrently herewith, entitled "Ink Compositions With Liposomes Containing Photochromic Compounds," with the named inventors Carol A. Jennings, Marcel P. Breton, Mary A. Isabella, Eric G. Johnson, Trevor I. Martin, and John F. Oliver, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises an aqueous liquid vehicle, a photochromic material, and a vesicle-forming lipid, wherein vesicles of the lipid are present in the ink.
Copending application U.S. Ser. No. 08/567,456, now U.S. Pat. No. 5,551,973, filed concurrently herewith, entitled "Photochromic Microemulsion Ink Compositions," with the named inventors John F. Oliver, Trevor I. Martin, Carol A. Jennings, Eric G. Johnson, and Marcel P. Breton, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises an aqueous phase, an oil phase, a photochromic material, and a surfactant, said ink exhibiting a liquid crystalline gel phase at a first temperature and a liquid microemulsion phase at a second temperature higher than the first temperature.
Copending application U.S. Ser. No. 08/567,589, filed concurrently herewith, entitled "Photochromic Electrostatic Toner Compositions," with the named inventors Trevor I. Martin, Carol A. Jennings, Eric G. Johnson, and John F. Oliver, the disclosure of which is totally incorporated herein by reference, discloses a toner composition for the development of electrostatic latent images which comprises particles comprising a mixture of a resin and a photochromic material. Another embodiment of the invention is directed to a liquid developer composition for the development of electrostatic latent images which comprises a nonaqueous liquid vehicle and a photochromic material, wherein the liquid developer has a resistivity of from about 10.sup.8 to about 10.sup.11 ohm-cm and a viscosity of from about 25 to about 500 centipoise. Yet another embodiment of the invention is directed to a liquid developer composition for the development of electrostatic latent images which comprises a nonaqueous liquid vehicle, a charge control agent, and toner particles comprising a mixture of a resin and a photochromic material.
The present invention is directed to hot melt ink compositions suitable for ink jet printing. In one embodiment, the inks are particularly suitable for thermal ink jet printing. A need exists for hot melt inks that result in images needing no further fixing or fusing treatment, such as drying or heating. There is also a need for hot melt inks with photochromic characteristics. In addition, there is a need for processes for preparing documents with images having photochromic characteristics. Further, there is a need for processes and materials which enable the placement of encoded information on documents which is not detectable to the reader but which is machine readable.